A couple of things to consider...the first of which is to remedy the soggy foam. That in itself will get you a NOTICEABLE improvement in perceived power. We had a 21' Thunderbird Formula with a soggy deck. Tore it out and replaced it...WOW, what a difference. Second is hull design. Adding a bunch more speed on a hull not designed for it MIGHT lead to stability issues. Trim Tabs on a shaft drive will help your hole shot, but they won't get any more of the wetted surface out of the water when the hull is up on plane. Are you going to use the boat for skiing? If so, replacing the soaked foam will get you into great skiing range....without spending unnecessary money on the engine. If it ain't broke, don't fix it...however, you MIGHT consider a roller cam/lifters. You'll get more of what you're looking for with a roller. As far as top end, I guess you don't HAVE to run it full (6,500 RPM) throttle if stability becomes an issue...
